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Zika causes birth defects regardless of trimester

A new CDC study found 5% of infants or fetuses born to women in the U.S. with laboratory-confirmed Zika infections had microcephaly or another Zika-linked birth defect.

"The bottom line is that Zika infection, identified during any trimester of pregnancy, can lead to serious brain and other birth defects," said Peggy Honein, an author on the study.

What they found: Infants developed microcephaly and other birth defects regardless of whether or not the mother displayed symptoms. The data also showed that babies infected in all trimesters exhibited birth defects, but the earlier the infection occurred, the more likely they were. Rates ranged from 8% for infants infected in the first trimester to 4% in the third.

Unanswered questions: There are reported cases of Zika-infected mothers having babies that appear normal at birth, but develop microcephaly and neurological difficulties as they age. Because this study looked at newborns, these cases are not included.

Go deeper: Much of the research linking Zika to microcephaly has been done in South America. This study confirms that those cases were due to the Zika virus, and not due to an interaction of the virus with something genetic or environmental in the area. The size (2549 people) and rigor of the study was also important, as past research on Zika-related birth defects has ranged in quality and given prevalence rates ranging from 1-13%. This was one of the first studies to break down infections by trimester and whether or not the mother was asymptomatic.